Just take the half of a dark circle and half of a light circle left over from the first quarter moon you made.

只取你制作的第一弦月留下的半个黑圈和半个亮圈。

The first quarter moon is sometimes called the half moon because it appears to us that half of the moon is illuminated, but it is called 'first quarter' because the moon is one-quarter of the way through its cycle.

上弦月有时被叫做半月，因为看上去只有一半月球是亮的，但是它被叫做上弦月，因为这时月亮在整个循环里走了四分之一。